1. Field
The disclosed subject matter relates to a method and apparatus for testing a vehicle for various structural noise and vibration transmission. More specifically, the disclosed subject matter relates to a method and apparatus for testing or monitoring wheel vibration through the use of a force/vibration input and unique attachment/damping structures for the vehicle to be tested. Even more specifically, the disclosed subject matter is directed to an excitation test method for reproducing vehicle chassis and steering wheel vibrations induced by brake torque fluctuation and/or tire mass imbalance.
2. Brief Description of the Related Art
A vehicle's suspension system affects both riding comfort and general performance in a vehicle. The suspension system is typically tested during the development the vehicle. Conventionally, a vehicle suspension system has been tested either by driving the vehicle on a road or by using an actuator. The latter can be carried out by placing the wheel(s) of a vehicle on an exciting unit and exciting the body by using an actuator to simulate road conditions. The body is supported by the wheels and the performance of the suspension system is evaluated by measuring the body motion. For example, a vibration input having a waveform such as obtained by an actual vehicle can be reproduced by an actuator and applied to the wheels of the vehicle. Measurement of vibration and movement at the vehicle's wheels, body and/or suspension can then be analyzed and compared to the input to determine vehicle characteristics.
Another vehicle excitation testing system includes using a so-called active suspension testing system in which rollers are driven by an actuator so as to simulate irregularities of a road in a chassis dynamometer for driving an actual vehicle on a bench of the rotating rollers.
FIG. 4 shows a conventional example of a vehicle testing system in which a dummy vehicle is outfitted with second actuators 904 fixed to a rigid wall 903 and reaction measuring devices 906 mounted to a frame 905. Wheels 902 are anchored to one end of a suspension system 901 of the vehicle and are linked to first actuators 907 that are fixed to bases 908. The other end of the suspension system 901 includes springs 971, shafts 972, and a frame 973. The reaction measuring device 906 measures reaction force applied to the dummy vehicle body from the suspension system 901.
The vehicle tests described above can be used only under certain conditions in which several parameters (e.g., body structure, road surface condition, running condition, etc.) are all predetermined. Thus, it has been difficult to apply the results of these experiments to the evaluation of other conditions. In addition, recently developed active suspension systems which introduce a feedback signal to a controller of a suspension, enlarge the scale of the test because the actual vehicle is used in the testing. The same applies also in the case of excitement testing. Since the active suspension system requires information from operating feedback signals, those exciting methods which do not provide such feedback information are unable to deal with these new active suspension systems.
There are mainly three types of excitation test methods. The first type is chassis dynamometer excitation. According to this method, the front wheels of a vehicle are driven by a chassis dynamometer. A vibrational input is realized by providing an off-center mass on the wheel or by providing an unevenly worked brake pad or caliper, etc.
The second method can be described as contact patch excitation. In this method, the front wheels of the vehicle are typically placed on an air bearing and the bearing is connected to a vibrator. The vehicle is excited through the air bearing by use of a vibrator.
In accordance with the third typical method, an angular shaking ramp is provided. The vehicle is placed on the angular shaking ramp with the front wheels located at a specific patch location. The patch location is then excited by a vibrator mechanism.
Vehicle chassis and steering wheel vibrations caused by tire/wheel imbalance is commonly referred to as “steering shimmy” and the vibration caused by braking torque fluctuation is called “brake judder.” The transfer path for the steering shimmy and brake judder can include the tires, suspension, steering system, and sometimes body flexibility, etc. Vibration is either strengthened or weakened due to subsystems' resonance (and chassis design) along the transfer path (from the tire(s) to the steering wheel). Thus, an excitation test method typically tries to take into account and analyze all possible subsystems (and chassis components) that might be contributing to the resonance of vibration. However, normal on-road testing for steering shimmy and brake judder is not repeatable and is not stable. This is due to road surface variations, phasing of tires, environmental conditions, etc. The typical on-road test is also time consuming and non-repeatable.
Accordingly, there has been a long sought need for a vehicle testing method and apparatus which allows performance testing of the suspension and chassis systems to be carried out accurately, at low cost, and with simple operation. The testing apparatus and method should be compatible with both static and active vehicles suspension systems, and provide repeatable vibration data. Measurement results can be used for many purposes including, but not limited to, mechanism investigation, analysis of chassis vibration characteristics, factor analysis, countermeasure confirmation, etc.